Radioimmunoassay of bound and free melatonin in plasma

We describe a nonextraction procedure, and two extraction procedures, for RIA of melatonin in human plasma. All procedures showed a diurnal rhythm of melatonin in human subjects, with interindividual differences greater than interprocedure differences. However, further investigations demonstrated co...

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Bibliographic Details
Published in:Clinical chemistry (Baltimore, Md.) Md.), 1998-02, Vol.44 (2), p.304-310
Main Authors: Di, Wei-Li, Kadva, Aban, Djahanbakhch, Ovrang, Silman, Robert
Format: Article
Language:English
Subjects:
Analytical, structural and metabolic biochemistry
Biological and medical sciences
Circadian Rhythm - physiology
Cross Reactions
Fatty acids
Fundamental and applied biological sciences. Psychology
Hormones and neuropeptides. Regulation
Humans
Hypothalamus. Hypophysis. Epiphysis. Urophysis
Lipids
Melatonin - blood
Melatonin - physiology
Other biological molecules
Protein Binding
Radioimmunoassay - methods
Serum Albumin - metabolism
Statistics as Topic
Time Factors
Vertebrates: endocrinology
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Summary:We describe a nonextraction procedure, and two extraction procedures, for RIA of melatonin in human plasma. All procedures showed a diurnal rhythm of melatonin in human subjects, with interindividual differences greater than interprocedure differences. However, further investigations demonstrated considerable variability of recovery in the nonextraction procedure, suggesting a variability of binding proteins between samples. Combining recovery and dialysis experiments in the extraction procedures, we demonstrated that chloroform was unable to extract albumin-bound melatonin from a human serum albumin solution but, paradoxically, was able to extract bound and free melatonin from a plasma sample. The methanol extraction procedure extracted free and bound melatonin from all sources. These results indicate that albumin binding can substantially affect the RIA procedures. We conclude that assays should be validated against free and bound melatonin and that the two forms should be independently investigated when assessing bioactivity.
ISSN:0009-9147
1530-8561
DOI:10.1093/clinchem/44.2.304